It is proposed to identify, purify and immunochemically characterize the major outer membrane protein antigens of Chlamydia trachomatis. Studies will focus on identifying surface antigens responsible for serotype specificity and immunodominant antigens of species or subspecies specificity that have potential usefulness in the development of sensitive assays for the immunodiagnosis of human chlamydial infections. The outer membrane complex of six serologically different chlamydial strains will be selectively extracted from purified organisms for physicochemical and immunological analysis. Comparative sodium dodecyl sulfate polyacrylamide slab gel electrophoresis will be used to identify and characterize major polypeptides of the extracted complex among chlamydial strains. Crossed immunoelectrophoresis (CIE) will be used to analyze outer membrane antigens. Modifications of CIE (intermediate gel and mixed antibody techniques) will be used to determine the strain and species specificity of outer membrane antigens. Absorption experiments combined with CIE and specific surface radio-labeling methods will be employed to determine the precise location of selected antigens. Antigens of particular interest will be excised for CIE electropherograms as agarose gel precipitates and will be used as immunogen to prepare monospecific antiserum. The gamma-globulin of monospecific antiserum will be used to prepare immunoadsorbent columns for the preparative isolation of homologous antigen from crude outer membrane extracts. Purified antigen will be characterized according to molecular weight, charge and general chemical composition.